Liquid repellent surfaces

ABSTRACT

A surface can be coated with a liquid repellent coating. Materials for making the liquid repellent coating (e.g., a fingerprint resistant coating) can be selected on the basis of surface energy considerations, such as a receding surface energy. The materials can include a polymer and a liquid repelling material, for example, poly(ethyl methacrylate) and a fluorinated silsesquioxane such as fluorodecyl POSS.

CLAIM OF PRIORITY

This application is a Continuation of U.S. patent application Ser. No.13/734,446 (now U.S. Pat. No. 9,650,518, issued on May 16, 2017), filedJan. 4, 2013, which claims priority to provisional U.S. PatentApplication No. 61/583,826, filed Jan. 6, 2012, each of which isincorporated by reference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No.FA9300-09-C-0023 awarded by the U.S. Air Force. The government hascertain rights in this invention.

TECHNICAL FIELD

This invention relates to liquid repellent surfaces.

BACKGROUND

The smudging of surfaces, particularly of smooth surfaces, byfingerprints is a problem that is growing in importance as touchscreendevices proliferate. Touchscreen surfaces that are resistant to thetransfer or smudging of fingerprints are desirable for aesthetic andtechnological reasons. Surface coatings can impart desirable propertiesincluding resistance to fingerprint transfer, high transmission, lowhaze, and robustness to repeated use. A fingerprint resistant surfaceshould be resistant to both water and oil transfer when touched by skin.Such a surface should be both hydrophobic and oleophobic, or at theextremes, superhydrophobic, and/or superoleophobic.

SUMMARY

An attractive strategy for mitigating the fingerprinting problem is todeposit a coating of optically transparent oleophobic materials thatresist wetting by the oils that are commonly found on human skin. Thegoal is to have the oils stick more strongly to the skin than they do tothe coated surface, such that they are not transferred to the coatedsurface upon contact. Similarly, it can be advantageous to have the oilsstick more strongly to a second surface (e.g., that of a wipe) than tothe coated surface, thereby facilitating removal of oils from the coatedsurface. Selecting materials that will impart a desired surface energycan be important in forming a fingerprint resistant coating. Inparticular, the coating desirably has a low surface energy as calculatedfrom receding liquid contact angles (referred to as a receding surfaceenergy).

In one aspect, a method of making a liquid repellent coating on asurface includes selecting a polymer and a liquid repelling materialbased on a measured surface energy of a coating including the polymerand the liquid repelling material; combining the selected polymer andthe selected liquid repelling material to form a mixture; and contactingthe mixture with the surface to form a coating including the selectedpolymer and the selected liquid repelling material on the surface.

The surface can be a nominally smooth surface. In other words, thesurface can be one that does not include any engineered texturalfeatures (such as nano- or micro-sized textural features adapted fortheir surface-modifying effects). Thus the surface can be, for example,smooth glass or plastic, such as might be found on a display screen ortouchscreen. However, the surface is not required to be nominallysmooth. Textured surfaces having the liquid repellent coating can alsohave the desired liquid repelling properties. The liquid repellingmaterial can include, for example, a small molecule, a nanoparticle, apolymer, or a combination thereof.

In some cases, the liquid repelling material can be enriched at thecoating-air interface. In other words, when forming the coating, theliquid repelling material tends to be located preferentially toward theair-coating interface rather than being uniformly distributed throughthe thickness of the coating. The coating can show good surfaceadhesion, such that it is not easily removed from the surface onceformed. In other circumstances, the coating can be peeled away from thesurface on which it is initially formed, which can be useful when, forexample, the coating is desirably removable or transferrable to anothersurface.

The measured surface energy can be a receding surface energy. Themeasured receding surface energy can be γ_(sv,r), γ_(sv,r) ^(d),γ_(sv,r) ^(p), γ_(sv,r) ⁺, or γ_(sv,r) ⁻. The measured receding surfaceenergy, γ_(sv,r), can be no greater than 50 mN m⁻¹, no greater than 20mN m⁻¹ , or no greater than 15 mN m⁻¹. The method can further includemeasuring a surface energy of a coating including a polymer and a liquidrepelling material prior to selecting. Combining can include combiningthe selected polymer and the selected liquid repelling material in apredetermined ratio.

The coating can be a fingerprint-resistant coating. The coating can betransparent and optically clear. The surface can be transparent. Thenanoparticles can include a fluorinated silsesquioxane. The fluorinatedsilsesquioxane can be fluorodecyl polyhedral oligomeric silsesquioxane(fluorodecyl POSS). The polymer can be poly(methyl methacrylate) (PMMA),poly(ethyl methacrylate) (PEMA), poly(butyl methacrylate) (PBMA), afluoropolymer, or a combination thereof. Contacting the mixture with thesurface can include spin coating.

Other aspects, embodiments, and features will be apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing depicting the chemical structure of fluorodecylPOSS.

FIG. 2 is a plot of term in S_(α) that contain θ and influence the dropwidth,

${w\left( {{i.e.},\frac{\sin \; \overset{\_}{\theta}}{\left( {2 - {3\; \cos \; \overset{\_}{\theta}} + {\cos^{3}\overset{\_}{\theta}}} \right)^{1/3}}} \right)},$

as a function of θ.

FIG. 3 are drawings depicting the chemical structures of polymers thatcan be blended with fluorodecyl POSS.

FIGS. 4A and 4B are scanning electron micrographs of films of “rough”fluorodecyl POSS and 80/20 PMMA/fluorodecyl POSS spin cast onto siliconwafers, respectively. AFM analysis of 1 μm×1 μm areas of the surfacesyielded root-mean square roughness, R_(q), of (a) R_(q)=86 nm (b)R_(q)=2.6 nm.

FIGS. 5A-5D are graphs showing advancing and receding contact anglesθ_(adv) and θ_(rec) for drops of water (γ_(lv)=72.1 mN/m) on all of thetested polymer/fluorodecyl POSS surfaces (FIG. 5A); θ_(adv) and θ_(rec)for drops of ethylene glycol (γ_(lv)=47.7 mN/m) on the PMMA/fluorodecylPOSS and TECNOFLON/fluorodecyl POSS materials (FIG. 5B); θ_(adv) andθ_(rec) for drops of dimethyl sulfoxide (γ_(lv)=44.0 mN/m) on thePMMA/fluorodecyl POSS and TECNOFLON/fluorodecyl POSS samples (FIG. 5C);and liquid wettability diagram for water and dimethyl sulfoxide on thePMMA/fluorodecyl POSS and TECNOFLON/fluorodecyl POSS blends (FIG. 5D).

FIGS. 6A-6D are graphs showing advancing and receding contact anglesθ_(adv) and θ_(rec) for drops of diiodomethane (γ_(lv)=50.8 mN/m) on allof the tested polymer/fluorodecyl POSS surfaces (FIG. 6A); θ_(adv) andθ_(rec) for drops of rapeseed oil (γ_(lv)=35.5 mN/m) on thePBMA/fluorodecyl POSS and PMMA/fluorodecyl POSS surfaces (FIG. 6B);θ_(adv) and θ_(rec) for drops of hexadecane (γ_(lv)=27.5 mN/m) on thePBMA/fluorodecyl POSS and PMMA/fluorodecyl POSS materials (FIG. 6C);nonpolar liquid wettability diagram for diiodomethane and hexadecane onthe PMMA/fluorodecyl POSS and PBMA/fluorodecyl POSS blends (FIG. 6D).

FIGS. 7A and B are photographs of diiodomethane droplets on 80/20PBMA/fluorodecyl POSS. The photograph of FIG. 7A was captured as liquidis syringed into the droplet, showing the contact angle approaches 141°.The photograph of FIG. 7B was captured as sufficient liquid is added,and the drop quickly advances forward to a contact angle of 95°. Thissporadic motion is repeated as additional diiodomethane is syringed intothe droplet.

FIGS. 8A-8D are graphs depicting XPS data acquired for spin-cast filmsof 80/20 PEMA/fluorodecyl POSS (FIGS. 8A and 8B) and 80/20TECNOFLON/fluorodecyl POSS (FIGS. 8C and 8D). Survey spectra for the80/20 PEMA/fluorodecyl POSS and 80/20 TECNOFLON/fluorodecyl POSS, FIGS.8A and 8C, respectively, have elemental peaks corresponding to F, O, andC labeled. High resolution carbon 1 s spectra for 80/20 PEMA/fluorodecylPOSS and 80/20 TECNOFLON/fluorodecyl POSS, FIGS. 8B and 8D, respective,have peaks corresponding to various carbon moieties located near thesurface are labeled.

FIGS. 9A-9D are graphs depicting the receding and advancing solidsurface energy terms as the fluorodecyl POSS content of the blends isincreased. FIG. 9A illustrates the advancing and receding surface energyterms, γ_(sv,α) and γ_(sv,r), for the PMMA/fluorodecyl POSS andPBMA/fluorodecyl POSS blends. FIG. 9B illustrates γ_(sv,α) and γ_(sv,r)for the PMMA/fluorodecyl POSS and TECNOFLON/fluorodecyl POSS materials.FIG. 9C illustrates the contributions to receding surface energy,γ_(sv,r) ^(p), for the PMMA-based and TECNOFLON-based samples. FIG. 9Dillustrates γ_(sv,r) ⁺, for the PMMA/fluorodecyl POSS andTECNOFLON/fluorodecyl POSS surfaces.

FIGS. 10A and 10B are photographs of microscope slides placed over afuchsia background. The slides were spin-coated with 80/20PEMA/fluorodecyl POSS and fluorodecyl POSS, corresponding to FIGS. 10Aand 10B, respectively. The coating in FIG. 10A is optically transparentand clear while the white fluorodecyl POSS powder is visible in FIG.10B.

FIG. 11A and 11B are photographs of silicon wafers that were coated with80/20 TECNOFLON/fluorodecyl POSS (FIG. 11A) and 80/20 PEMA/fluorodecylPOSS (FIG. 11B) and subjected to cross-cut adhesion tests. The ASTMcategorizations of strengths of adhesion of these coatings are 1B (lowadhesion) and 5B (highest adhesion), respectively.

FIG. 12A-12D are photographs of bare glass, PEMA-coated glass, 95/5PEMA/fluorodecyl POSS-coated glass, and 80/20 PEMA/fluorodecylPOSS-coated glass, respectively, all subjected to the stearic acidfingerprinting test protocol described above. The 80/20 PEMA/fluorodecylPOSS surface of FIG. 12D clearly resists smudging by fingerprints morestrongly than the bare glass substrate of FIG. 12A.

DETAILED DESCRIPTION

Surfaces that resist wetting by liquids are of interest for a widevariety of applications, including ink release surfaces for printers,seals/gaskets, stain-resistant fabrics, and fingerprint resistance. See,for example, U.S. Patent Application Publication No. 2011/0025752; S. T.Iacono et al., J. Mater. Chem., 2010, 20, 2979-2984; A. Vilcnik et al.,Langmuir, 2009, 25, 5869-5880; S. S. Chhatre et al., Langmuir 2009, 25,13625-13632; W. Choi et al., Adv. Mater. 2009, 21, 2190-2195; W. Ming etal., Contact Angle, Wettability Adhes., 2009, 6, 191-205; Y. Gao et al.,Polymer, 2010, 51, 5997-6004; and R. Misra et al., J. Appl. Polym. Sci.,2010, 115, 2322-2331, each of which is incorporated by reference in itsentirety.

Surfaces can be coated with polymers having perfluorocyclobutane rings,fluorochemicals, fluorinated organosilane polymers, or fluoropolymernanoparticles. See, for example, U.S. Pat. No. 7,332,217; U.S. Pat. No.7,288,282; U.S. Pat. No. 7,638,581; International ApplicationPublication No. WO 2010/0129624; and EP Publication No. 00490335, eachof which is incorporated by reference in its entirety.

The wettability (or, conversely, repellency) of a substrate is sensitiveto both topographical texture and surface chemistry. See, for example,R. N. Wenzel, J. Ind. Eng. Chem., 1936, 28, 988-994; A. B. D. Cassie andS. Baxter, Trans. Faraday Soc., 1944, 40, 546-551; and R. E. Johnson,Jr. and R. H. Dettre, Surfactant Sci. Ser., 1993, 49, 1-73, each ofwhich is incorporated by reference in its entirety. Textured surfaceswith appropriately designed chemistries and features may impart “superliquid repellency” by trapping air in the surface asperities underneath“Cassie state” liquid droplets. These textured substrates are commonlycalled “superhydrophobic” when they support Cassie state water dropletswith contact angles above 150° and less than 10° of contact anglehysteresis, and “omniphobic” when both water and lower surface tensionliquids, such as alkanes, adopt Cassie configurations with the samecontact angle limitations. See, for example, A. Lafuma and D. Quere,Nat. Mater., 2003, 2, 457-460; X. J. Feng and L. Jiang, Adv. Mater.,2006, 18, 3063-3078; A. Tuteja et al., Proc. Natl. Acad. Sci. U.S.A.2008, 105, 18200-18205; and S. S. Chhatre et al., Langmuir, 2010, 26,4027-4035, each of which is incorporated by reference in its entirety.

A commonly employed strategy for facilitating the formation of Cassiestate liquid droplets is to coat textured substrates with films of lowsurface energy materials; such a tactic is also widely used to reducethe liquid wettability of smooth surfaces. Zisman and colleaguesestablished that the surface energy values of chemical groups decreasein the order —CH₂—>—CH₃>—CF₂—>—CF₃, and substantial research effortshave focused on the development of coatings that enhance liquidrepellency by preferentially locating low energy moieties at or near thesolid-air interface. See, for example, W. A. Zisman, In Contact Angle,Wettability, and Adhesion; F. M. Fowkes, Ed.; Washington, D.C., AmericanChemical Society, 1964, Vol. 43; H. W. Fox and W. A. Zisman, J. ColloidSci., 1950, 5, 514-531; H. W. Fox and W. A. Zisman, J. Colloid Sci.,1952, 7, 109-121; M. J. Owen and H. Kobayashi, Macromol. Symp., 1994,82, 115-123; and S. R. Coulson et al., Chem. Mater., 2000, 12,2031-2038, each of which is incorporated by reference in its entirety.One class of materials that has recently received attention as a liquidrepellent material is polyhedral oligomeric silsesquioxanes (POSS). POSScompounds are thermally stable molecules comprised of silicon-oxygencores with organic groups attached to the apex of each silicon atom, andthey have found widespread application as additives to enhance the bulkproperties of polymer-POSS nanocomposites. See, for example, G. Z. Li etal., J. Inorg. Organomet. Polym., 2001, 11, 123-154 and S. H. Phillipset al., Curr. Opin. Solid St. Mater. Sci., 2004, 8, 21-29, each of whichis incorporated by reference in its entirety.

Recent investigations have demonstrated that POSS materials also holdpromise as surface modifiers. One particularly promising POSS compound,and the most liquid repellent of the POSS molecules described in theliterature to date, is (1H,1H,2H,2H-heptadeca-fluorodecyl)₈Si₈O₁₂, or“fluorodecyl POSS.” See, for example, S. T. Iacono et al., Chem.Commun., 2007, 4992-4994; J. M. Mabry et al., Angew. Chem., Int. Ed.,2008, 47, 4137-4140; and S. S. Chhatre et al., ACS Appl. Mater.Interfaces, 2010, 2, 3544-3554, each of which is incorporated byreference in its entirety.

FIG. 1 shows the structure of fluorodecyl POSS. Droplets of liquids witha range of surface tension values (15.5 mN/m≤γ_(lv)≤72.1 mN/m)systematically form higher advancing and receding contact angles on flatfilms of fluorodecyl POSS than they do on coatings of alternative POSSspecies or on commercial fluoropolymers, such as TECNOFLON or TEFLON.The high liquid contact angles adopted by droplets on fluorodecyl POSScoatings are attributed to a synergistic combination of the rigidsilicon-oxygen cage and the long fluorodecyl side chains.

There is little consensus in the literature as to specific attributesthat categorize a substrate as “liquid repellent,” “hydrophobic,” or“oleophobic.” Often single static contact angles of probe liquids areused to provide some quantification of the wettability of a surface.Static contact angles generally fail to adequately describe the wettingbehavior of liquid drops on surfaces, however, and characterizingwettability on the basis of such measurements is of limited utility.See, for example, L. C. Gao and T. J. McCarthy, Langmuir, 2008, 24,9183-9188; L. C. Gao and T. J. McCarthy, Langmuir, 2009, 25,14105-14115; and M. Strobel and C. S. Lyons, Plasma Processes Polym.,2011, 8, 8-13, each of which is incorporated by reference in itsentirety.

Surface geometry can impart liquid repellant properties to surfaces,including in some cases super-oleophobic properties. Liquid repellentsurfaces can be formed over surfaces having a smooth surface topography,or a textured topography (e.g., a nanotextured topography). In somecases a super-oleophobic surface can make use of a geometry in which thesurface has a protrusion portion and a re-entrant portion. Thisflexibility can allow surfaces having multiple desirable properties tobe produced, for example, a surface that is both hydrophobic andoleophobic, and in some cases, both super-hydrophobic andsuper-oleophilic. Such a surface has been produced and is an excellentoil-water separator. See, for example, U.S. Patent ApplicationPublication No. 2010/0316842, which is incorporated by reference in itsentirety.

The methods and surfaces described here can have certain advantages andimprovements over other methods of surface modification. For example,super-oleophobic surfaces, i.e., surfaces which are resistant to eventhe lowest surface tension liquids like decane and octane, can beproduced. A re-entrant surface curvature is an optional feature forcreating a super-oleophobic surface.

There are a number of different commercial applications for the varioustypes of surfaces produced in this work. The surfaces can be a portionof any article, including a vehicle, equipment, a tool, constructionmaterial, a window, a flow reactor, a textile, or others. A fewapplications for each surface include the following.

Super-hydrophobic and super-oleophilic surfaces can be ideal foroil-water separation, which has a number of useful applications,including waste water treatment and cleaning up oil spills. Otherapplications include cleaning of ground water, oil well extractions,biodiesel processing, mining operations, and food processing.

Super-oleophobic surfaces can be resistant to dust, debris, and inparticular, resistant to fingerprints. Such surfaces are thereforeuseful as a coating on lenses, computer screens, tablet computers,personal data assistants, and other displays and handheld devices.Super-oleophobic surfaces can also be used as anti-graffiti,self-cleaning surfaces. Super-oleophobic surfaces can also be of greatuse in the petroleum industry. For example, various surfaces that areattacked by the petroleum products could be lined with super-oleophobiccoatings, preventing their degradation, for example, providing swellresistance to organic materials on fabrics. Also, super-oleophobiclinings can be used as a drag reducer in various pipelines.

A number of surfaces in nature use extreme water repellency for specificpurposes; be it water striding or self-cleaning. A number of surfacesencountered in nature are superhydrophobic, displaying water (surfacetension γ=72.1 mN/m) contact angles (WCA) greater than 150°, and lowcontact angle hysteresis. The most widely-known example of asuperhydrophobic surface found in nature is the surface of the lotusleaf. It is textured with small 10-20 μm-sized protruding nubs, whichare further covered with nm-size epicuticular wax crystalloids. See, forexample, W. Barthlott and C. Neinhuis, Planta, 1997, 202, 1-8. Numerousstudies have shown that it is this combination of surface chemistry plusroughness on multiple scales—micron and nanoscale that imbues superhydrophobic character to the lotus leaf surface. The effects of surfacechemistry and surface texture can be controlled to create high levels ofoil-repellency and super-oleophobic behavior.

Surface curvature can be used as a third factor, apart from surfaceenergy and roughness, to modify surface wettability. The surfacecurvature (apart from surface chemistry and roughness), can be used tosignificantly enhance liquid repellency, as exemplified by studyingelectrospun polymer fibers containing very low surface energyperfluorinated molecules (FluoroPOSS). Increasing the POSS concentrationin the electrospun fibers can systematically transcend fromsuper-hydrophilic to super-hydrophobic and to the super-oleophobicsurfaces (exhibiting low hysteresis and contact angles with decane andoctane greater than 150°). See, for example, U.S. Patent ApplicationPublication No. 2010/0316842, which was incorporated by reference in itsentirety, above.

Liquid repelling materials can have hydrophobic and/or oleophobicproperties. A liquid repelling material can include halogenated orperhalogenated groups (e.g., fluorinated or perfluorinated groups), forexample, fluorinated or perfluorinated organic moieties having between 1and 20 carbon atoms, in particular, C₂-C₁₈ alkyl chains, which can besubstituted or unsubstituted. The alkyl chains can be substituted withone or more halogens; in some cases the alkyl chains can be nearlyperhalogenated or fully perhalogenated. The liquid repelling materialcan include a silsesquioxane having one or more alkyl chains, which canbe halogenated, e.g., nearly perhalogenated or fully perhalogenated.

A class of fluorinated polyhedral oligomeric silsesquioxanes (POSS)molecules has been developed in which the rigid silsesquioxane cage issurrounded by fluoro-alkyl groups. A number of different molecules withdifferent organic groups, including 1H,1H,2H,2H-heptadecafluorodecyl(referred to as fluorodecyl POSS) and 1H,1H,2H,2H-tridecafluorooctyl(fluorooctyl POSS) are available, and this class of materials is denotedgenerically as fluoroPOSS. The fluoroPOSS molecules contain a very highsurface concentration of fluorine containing groups, including —CF₂— and—CF₃ moieties. The high surface concentration and surface mobility ofthese groups, as well as the relatively high ratio of —CF₃ groups withrespect to the —CF₂— groups, results in one of the most hydrophobic andlowest surface energy materials available today. See, for example, M. J.Owen and H. Kobayashi, Macromol. Symp., 1994, 82, 115-123. A spin coatedfilm of fluorodecyl POSS on a Si wafer has an advancing and recedingwater contact angle of 124.5±1.2°, with an rms roughness of 3.5 nm.Blends of a moderately hydrophilic polymer, poly(methyl methacrylate)(PMMA, M_(w)=540 kDa, PDI about 2.2) and fluorodecyl POSS can be used invarious weight ratios to create materials with different surfaceproperties. Other polymers can be used in place of, or in combinationwith, PMMA. By varying the mass fraction of fluoroPOSS blended withvarious polymers, the surface energy of the polymer-fluoroPOSS blend canbe systematically changed. This can afford control over the advancingand receding contact angles of the blends and provide a mechanism forsystematically studying the transition from the Wenzel to the Cassiestate on surfaces made from the blends.

A more useful characterization of wettability can be completed byconsidering the two physical processes by which sessile liquid drops canbe removed from substrates. First, a surface can be tilted (or,alternatively, rotated rapidly) to induce sliding or rolling of asessile liquid drop. See, for example, C. W. Extrand and A. N. Gent, JColloid Interface Sci., 1990, 138, 431-442, which is incorporated byreference in its entirety. The angle of tilt required to induce dropmotion (α) does not correlate with any single measured contact angle,but can be predicted using measured receding and advancing contactangles, θ_(rec) and θ_(adv), and an equation proposed by Furmidge thatis consistent with experimental data. See, for example, H. Murase, etal. J. Appl. Polym. Sci., 1994, 54, 2051-2062; C. Della Volpe, et al.Langmuir, 2002, 18, 1441-1444; L. Feng, et al. Langmuir, 2008, 24,4114-4119; C. G. Furmidge, J. Colloid Sci., 1962, 17, 309-324; and E.Wolfram and R. Faust, In Wetting, Spreading, and Adhesion, London,Academic Press, 1978, 213-222, each of which is incorporated byreference in its entirety.

$\begin{matrix}{{\sin (\alpha)} = {\frac{\gamma_{lv}}{m\; g}{w\left( {{\cos \; \theta_{rec}} - {\cos \; \theta_{adv}}} \right)}}} & (1)\end{matrix}$

where m is the mass of the drop, g is the gravitational constant, γ_(lv)is the liquid-vapor surface tension of the liquid, and w is the width ofthe drop perpendicular to the drop sliding direction. The sliding angle,α, clearly depends on the dimensionless contact angle hysteresis (CAH)in the form (cos θ_(rec)−cos θ_(adv)), not on a single contact anglevalue. This hysteresis term is not, however, the only parameter inEquation 1 that is sensitive to the liquid contact angles; the dropwidth, w, also varies with liquid contact angles and may be estimatedusing the expression:

$\begin{matrix}{w \approx {2\left( \frac{3\; V}{\pi} \right)^{1/3}\frac{\sin \; \overset{\_}{\theta}}{\left( {2 - {3\; \cos \; \overset{\_}{\theta}} + {\cos^{3}\overset{\_}{\theta}}} \right)^{1/3}}}} & (2)\end{matrix}$

where Vis the drop volume and θ is a cosine-averaged apparent contactangle that can be computed form the expression cos θ=½(cos θ_(adv)+cosθ_(rec)). See, for example, W. Choi et al., J. Colloid Interface Sci.,2009, 339, 208-216, which is incorporated by reference in its entirety.Defining density as ρ−m/V and substituting the expression for w fromEquation 2 into Equation 1 yields:

$\begin{matrix}{{\sin \; \alpha} = {{\frac{2\; \gamma_{lv}}{\rho \; g}\left( \frac{3}{\pi \; V^{2}} \right)^{1/3}\frac{\sin \; {\overset{\_}{\theta}\left( {{\cos \; \theta_{rec}} - {\cos \; \theta_{adv}}} \right)}}{\left( {2 - {3\; \cos \; \overset{\_}{\theta}} + {\cos^{3}\overset{\_}{\theta}}} \right)^{1/3}}} = {\frac{2\; \gamma_{lv}}{\rho \; g}\left( \frac{3}{\pi \; V^{2}} \right)^{1/3}S_{a}}}} & (2)\end{matrix}$

where the drop sliding scaling factor, S_(α), contains all of thecontact angle dependencies (i.e., those that are functions of theliquid-surface interactions) of the sliding angle, α. Sessile drops of agiven size and surface tension will slide at the lowest tilt angle, α,on surfaces characterized by small values of S_(α). This factor, S_(α),is primarily sensitive to contact angle hysteresis in the form (cosθ_(rec)−cos θ_(adv)) but also contains some dependency on the absolutemagnitudes of θ_(adv) and θ_(rec) due to the influence of θ on the dropwidth, w. The sensitivity of the sliding angle, α, to the mean contactangle, θ, reflects the fact that, all else equal, liquids characterizedby higher magnitude contact angles will form narrower cross-sectiondrops that slide more readily than the flatter sessile drops formed byliquids with smaller contact angles and larger contact areas.Quantitatively, these θ-containing terms modify the hysteresisdependency (cos θ_(rec)−cos θ_(adv)) by a numerical factor that isgenerally between 3(θ≈3°) and 0.1(θ≈170°). See, for example, W. Choi etal., J. Colloid Interface Sci., 2009, 339, 208-216, which isincorporated by reference in its entirety. FIG. 2 shows a complete plotof this functional dependence as θ varies.

A second method to physically remove a sessile liquid drop is to pullthe drop vertically off of a substrate. Such a process is often analyzedusing thermodynamic work arguments to account for the individual freeenergy changes associated with the pairwise formation and elimination ofspecific interfaces. The Young-Dupré equation is commonly used tocalculate the equilibrium work of adhesion (W_(e)), which is defined asthe reversible free energy associated with the creation and destructionof interfaces:

W _(e)=γ_(lv)(1+cos θ_(e))   (4)

where θ_(e) is the equilibrium (Young's) contact angle. See, forexample, T. Young, Philos. Trans. R. Soc. London, 1805, 95, 65; A.Dupre, Theorie Mecanique de la Chaleur, Paris, Gauthier-Villars, 1869;J. C. Berg, Surfactant Sci. Ser. 1993, 49, 75-148; and P. C. Hiemenz andR. Rajagopalan, Principles of Colloid and Surface Chemistry, New York,Marcel Dekker, 1997, each of which is incorporated by reference in itsentirety. There are several drawbacks to estimating the solid surfaceenergy, W_(e), using equilibrium (Young's) contact angle, θ_(e).Firstly, θ_(e) is difficult to measure and, perhaps more importantly,θ_(e) and, by extension, γ_(lv), do not typically correlate well withthe actual work required to remove liquid drops from substrates. See,for example, A. Marmur, Soft Matter, 2006, 2, 12-17 and A. Marmur, Annu.Rev. Mater. Res., 2009, 39, 473-489, each of which is incorporated byreference in its entirety. For example, the forces required to removeWilhelmy plates from liquids or to separate surfaces connected by acapillary bridge of water are dependent on the receding contact angle,θ_(rec), and not the equilibrium contact angle, θ_(e). It has beensuggested that the practical work of adhesion, W_(p), that correspondsto the actual work required to separate a liquid from a surface could becalculated using a modified version of Equation 4 that replaces θ_(e)with the receding contact angle, θ_(rec):

W _(p)=γ_(lv)(¹+cos θ_(rec))   (5)

See, for example, E. J. de Souza et al., Langmuir, 2008, 24, 1391-1396and K. L. Mittal, In Adhesion Measurement of Thin Films, Thick Films andBulk Coatings, Philadelphia, Pa., ASTM Special Tech. Publ. 640, 1976,each of which is incorporated by reference in its entirety.

The practical work required to remove a liquid drop from a surface isminimized when θ_(rec) is maximized and is not related explicitly to theidealized value of the equilibrium contact angle, θ_(e).

An alternative approach to using measurements of θ_(e) to estimateγ_(sv) is to utilize measurements of the advancing and receding contactangles, θ_(adv) and θ_(rec), to calculate an “advancing surface energy,”Y_(sv,α), and a “receding surface energy,” Y_(sv,r), for a test sample.See, for example, C. Della Volpe and S. Siboni, J. Colloid InterfaceSci., 1997, 195, 121-136, which has been incorporated by reference inits entirety. Advantageously, measurements of both θ_(adv) and θ_(rec),unlike those of θ_(e), are readily reproducible and, furthermore, arereliable predictors of the propensity for drop sliding described inEquation 3 or the ease of drop pull-off summarized in Equation 5. Thisadvancing/receding surface energy approach is not derived from anyfundamental theory, but can yield quantifiable and repeatable parametersthat provide an empirical characterization of the liquid repellency (or,conversely, wettability) of a smooth substrate with a given surfacechemistry.

Semi-empirical models of solid surface energy that are commonly fit tocontact angle data include those previously developed. See, for example,D. K. Owens and R. C. Wendt, J. Appl. Polym. Sci., 1969, 13, 1741-1747;L. A. Girifalco and R. J. Good, J. Phys. Chem., 1957, 61, 904-909; R. J.Good, J. Colloid Interface Sci., 1977, 59, 398-419; C. J. Van Oss, R. J.Good, and M. K. Chaudhury, Langmuir, 1988, 4, 884-891; C. J. Van Oss, M.K. Chaudhury, and R. J. Good, Chem. Rev., 1988, 88, 927-941; and R. J.Good, J. Adhes. Sci. Technol., 1992, 6, 1269-1302, each of which isincorporated by reference in its entirety.

According to the Girifalco-Good model, the total surface energy ofeither a solid (γ_(sv)) or a liquid (γ_(lv)) is the sum of thedispersion (or nonpolar, γ^(d)) and polar (γ^(p)) contributions. Thepolar portion can be further subdivided into hydrogen bond donating (oracidic, γ⁺) and hydrogen bond accepting (or basic, γ⁻) components:

γ_(lv)=γ_(lv) ^(d)+γ_(lv) ^(p)+2√{square root over (γ_(lv) ⁺γ_(lv) ⁻)}

γ_(sv)=γ_(sv) ^(d)+γ_(sv) ^(p)2√{square root over (γ_(sv) ⁺γ_(sv)⁻)}  (6)

The surface energy components of many probe liquids are known based onwater as a standard state with γ_(lv) ⁺=γ_(lv) ⁻=25.5 mN/m and some ofthese values are provided in Table 1. See, for example, M. K. Chaudhury,Mater. Sci. Eng. R, 1996, 16, 97-159, which has been incorporated byreference in its entirety.

TABLE 1 Values of total (γ_(lv)), dispersion (γ_(lv) ^(d)), polar(γ_(lv) ^(p)), hydrogen bond donating (γ_(lv) ⁺), and hydrogen bondaccepting (γ_(lv) ⁻) surface energies in mN/m. Liquid γ_(lv) γ_(lv) ^(d)γ_(lv) ^(p) γ_(lv) ⁼ γ_(lv) ⁻ Water 72.1 21.1 51.0 25.5 25.5 Ethylene47.7 28.7 19.0 1.9 47.0 Glycol Dimethyl 44.0 36.0 8.0 0.5 32.0 SulfoxideDiiodomethane 50.8 50.8 0.0 0.0 0.0 Rapeseed Oil 35.5 35.5 0.0 0.0 0.0Hexadecane 27.8 27.8 0.0 0.0 0.0

The expressions provided in Equation 6 can be combined with Equation 5(either as written, or with θ_(adv) substituted for θ_(rec)) to yieldexpressions for the advancing and practical works of adhesion, W_(α) andW_(p):

W _(α)=γ_(lv)(1+cos θ_(adv))=2(√{square root over (γ_(sv,α) ^(d)γ_(lv)^(d))}+√{square root over (γ_(sv,α) ⁺γ_(lv) ⁻)}+√{square root over(γ_(lv) ⁺γ_(sv,α) ⁻)})

W _(p)=γ_(lv)(1+cos θ_(rec))=2(√{square root over (γ_(sv,r) ^(d)γ_(lv)^(d))}+√{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)}+√{square root over(γ_(lv) ⁺γ_(sv,r) ⁻)})   (7)

Note that all of the energetic terms in these expressions are crossproducts between the solid and liquid parameters. See, for example, J.C. Berg, Surfactant Sci. Ser., 1993, 49, 75-148, which is incorporatedby reference in its entirety. The unknown quantities γ_(sv,i) ^(d),γ_(sv,i) ⁺, and γ_(sv,i) ⁻ can be calculated from measurements of theadvancing or receding contact angles of three contacting liquids and thefollowing linear system of equations:

$\begin{matrix}{{{2\begin{bmatrix}\sqrt{\gamma_{{lv},i,1}^{d}} & \sqrt{\gamma_{{lv},i,1}^{-}} & \sqrt{\gamma_{{lv},i,1}^{+}} \\\sqrt{\gamma_{{lv},i,2}^{d}} & \sqrt{\gamma_{{lv},i,2}^{-}} & \sqrt{\gamma_{{lv},i,2}^{+}} \\\sqrt{\gamma_{{lv},i,3}^{d}} & \sqrt{\gamma_{{lv},i,3}^{-}} & \sqrt{\gamma_{{lv},i,3}^{+}}\end{bmatrix}}\begin{bmatrix}\sqrt{\gamma_{{sv},i}^{d}} \\\sqrt{\gamma_{{sv},i}^{+}} \\\sqrt{\gamma_{{sv},i}^{-}}\end{bmatrix}} = \left\lbrack \begin{matrix}{\gamma_{{lv},i,1}\left( {1 + {\cos \; \theta_{i,1}}} \right)} \\{\gamma_{{lv},i,2}\left( {1 + {\cos \; \theta_{i,2}}} \right)} \\{\gamma_{{lv},i,3}\left( {1 + {\cos \; \theta_{i,3}}} \right)}\end{matrix} \right\rbrack} & (8)\end{matrix}$

This protocol was previously used to characterize spin-cast surfaces offluorodecyl POSS, which has an advancing surface energy,γ_(sv,α)=9.5±1.5 mN/m, and a receding surface energy, γ_(sv,r)=16.3±2.4mN/m.

These low values of γ_(sv,α) and γ_(sv,r) indicate that fluorodecyl POSSinteracts weakly with contacting liquids, and is a strongly “liquidrepellent” material with respect to both the sliding and pull-offmechanisms summarized in Equations 3 and 5, respectively. Despite theseunusually low surface energy values (particularly γ_(sv,r)), there areseveral drawbacks to employing pure fluorodecyl POSS as a liquidrepellent coating. First, the morphology of films composed ofcrystalline POSS molecules is sensitive to the deposition conditions,with both smooth and rough coatings being reported in the literature.See, for example, A. Tuteja et al., Science, 2007, 318, 1618-1622, whichhas been incorporated by reference in its entirety. For fully-wettedWenzel state droplets, increases in surface roughness generally lead todecreases in receding liquid contact angles and a concomitant increasein adhesion to the substrate, a detrimental result if maximum liquidrepellency is desired. Pure POSS films may also contain crystallitesthat are large enough to scatter light and reduce optical transparency,a drawback for numerous applications. Additionally, the weakintermolecular interactions that make fluorodecyl POSS coatings liquidrepellent also reduce the adhesion of deposited fluorodecyl POSS filmsto underlying substrates, limiting their abrasion resistance anddurability in coatings applications. Finally, POSS molecules aregenerally more expensive than alternative materials such as polymers,and minimizing the amount of fluorodecyl POSS that must be applied to asubstrate to impart maximum liquid repellency is beneficial.

The POSS molecules may be used as surface-modifying additives in blendswith polymers. The POSS molecules in such blends may bloom to thecomposite/air interface in order to lower the system free energy,imparting the composite material with at least some of the liquidrepellency characteristics of the POSS component. See, for example, S.Turri and M. Levi, Macromol. Rapid Commun., 2005, 26, 1233-1236, whichhas been incorporated by reference in its entirety. Researchers pursuingthis strategy have reported increases in liquid contact angles by addingvarious types of POSS molecules to polyurethanes, nylon 6,polycarbonate, poly(methyl methacrylate), poly(ethyl methacrylate),polypropylene, epoxy thermosets, poly(chlorotrifluoroethylene),fluoropolymer resin, perfluorocyclobutyl aryl ether polymers, and thecommercial fluoropolymer TECNOFLON BR9151. See, for example, R. Misra etal., J. Polym. Sci., Part B: Polym. Phys., 2009, 47, 1088-1102; P. F.Rios et al., J. Adhes. Sci. Technol., 2006, 20, 563-587; K. Koh et al.,Macromolecules, 2005, 38, 1264-1270; J. W. Xu et al., J. Mater. Chem.,2009, 19, 4740-4745; F. Mammeri et al., Chem. Mater., 2009, 21,4163-4171; A. Tuteja et al., MRS Bull., 2008, 33, 752-758; L. Z. Dai etal., Sci. China Chem., 2010, 53, 2000-2005; A. J. Meuler et al., ACSAppl. Mater. Interfaces, 2010, 2, 3100-3110; R. Misra et al., J. Polym.Sci. Part B: Polym. Phys., 2007, 45, 2441-2455; K. Zeng and S. Zheng, J.Phys. Chem. B, 2007, 111, 13919-13928; J. M. Mabry et al., In ACSSymposium Series 964; S. Clarson et al., Eds.; Washington, D.C.,American Chemical Society, 2007, 290-300; I. Jerman et al., Sol. EnergyMater. Sol. Cells, 2010, 94, 232-245; S. T. Iacono et al.,Macromolecules, 2007, 40, 9517-9522; and S. T. Iacono et al., Polymer,2007, 48, 4637-4645, each of which is incorporated by reference in itsentirety.

Blends of fluorodecyl POSS with the fluoropolymer TECNOFLON BR9151 andthree polymethacrylates with a broad range of glass transitiontemperatures: poly(methyl methacrylate) (PMMA, T_(g)=124° C.),poly(ethyl methacrylate) (PEMA, T_(g)=77° C.), and poly(butylmethacrylate) (PBMA, T_(g)=18° C.) were observed. These polymers areattractive candidates as matrix materials for polymer/fluorodecyl POSScomposites because they all readily dissolve in a fluorinated solvent(Asahiklin AK225) along with the fluorodecyl POSS. The molecularstructures of these four polymers are provided in FIG. 3. The advancingand receding contact angles of water, ethylene glycol, dimethylsulfoxide, diiodomethane, rapeseed oil, and hexadecane were measuredgoniometrically on all of the test surfaces and these values were thenused to evaluate advancing and receding surface energy values ofpolymer/fluorodecyl POSS blends within the context of the Girifalco-Goodframework. The lowest surface energy values and maximum liquidrepellencies are attained in PEMA or PMMA blends containing as little as20 wt % fluorodecyl POSS. Furthermore, these composite coatings arereadily deposited as smooth, optically transparent films that adherestrongly to underlying substrates.

EXAMPLES Materials

Asahiklin (AK225, Asahi Glass Company), ethylene glycol (99%, Aldrich),dimethyl sulfoxide (99%, Aldrich), diiodomethane (99%, Aldrich),rapeseed oil (Fluka), and hexadecane (99%, Aldrich) were used asreceived. Deionized water (18 MΩ-cm) was purified using a Milliporesystem. TECNOFLON BR9151 (Solvay Solexis), PMMA (Scientific PolymerProducts, M_(w)=540 kg/mol), PEMA (Aldrich, M_(w)=515 kg/mol), PBMA(Aldrich, M_(w)=337 kg/mol), Polycarbonate (PC, Bayer),1H,1H,2H,2H-perfluorodecyltrichlorosilane (Aldrich), and TEFLON AF-2400solution (DuPont, item number 400S2-100-1) were used as received. Manydifferent fluoropolymers are marketed under the “TEFLON” name. Theamorphous TEFLON AF-2400 is characterized by higher θ_(adv) and θ_(rec)and thus lower γ_(sv,α) and γ_(sv,r) than most other TEFLON materials,making it a minimum surface energy benchmark for TEFLON. See, forexample, L. C. Gao and T. J. McCarthy, Langmuir, 2008, 24, 9183-9188 andS. Lee, J. S. Park, and T. R. Lee, Langmuir, 2008, 24, 4817-4826, eachof which is incorporated by reference in its entirety. Fluorodecyl POSSwas prepared following established protocols.

Differential Scanning Calorimetry (DSC)

Calorimetry experiments were conducted using a TA Instruments QIOOO DSC.Approximately 5 mg of each polymer was placed into an aluminum pan,heated at 10° C./min to 180° C., cooled at 10° C./min to −80° C., andheated again at 10° C./min to 180° C. Data were acquired during thesecond heating cycle.

Coating Methodology

Polymer/fluorodecyl POSS solutions (total solids 20 mg/mL) were preparedby dissolving polymers and/or fluorodecyl POSS in Asahiklin.Dichloromethane was used to prepare the PC solution because PC is notsoluble in Asahiklin. Approximately 200 nm-300 nm thick coatings of testmaterials were deposited at room temperature on silicon wafers via aspin coating process; approximately 0.5 mL of solution was placed on topof each silicon wafer (approximately 4 cm²) and the wafer was spun at900 rpm for 30 seconds.

Amorphous TEFLON AF-2400 was deposited onto a silicon wafer by: (i)placing approximately 0.5 mL of solution on top of a silicon wafer(approximately 4 cm²) and spinning the wafer and 900 rpm for 30 seconds;(ii) heating the film overnight at approximately 250° C. to evaporatethe low-volatility fluorinated solvent.

Silicon wafers were treated with1H,1H,2H,2H-perfluorodecyltrichlorosilane by: (i) placing them, alongwith a few drops of the reactive fluoroalkylsilane liquid, inside aTEFLON canister under an inert nitrogen atmosphere; (ii) sealing thecanister and heating it overnight at 150° C.

Surface Characterization

Scanning electron microscopy (SEM) images were acquired using a JEOL6060 instrument operating at an acceleration voltage of 5 kV. Specimenswere sputter coated with approximately 2 nm of platinum prior toimaging. Atomic force microscopy (AFM) measurements were carried outusing a Dimension 3100 instrument (Veeco Metrology Group) operating inthe tapping mode. X-ray photoelectron spectroscopy (XPS) was performedusing a Kratos Axis Ultra X-ray photoelectron spectrometer manufacturedby Kratos Analytical (Manchester, England). The monochromatized Al Kαsource was operated at 15 kV and 10 mA (150 W) and emissions werecollected at takeoff vectors orthogonal to the sample surface.

Contact Angle Measurements

Contact angles of probe fluids on test surfaces were measured using aVCA2000 goniometer (AST Inc.). Advancing (θ_(adv)) and receding(θ_(rec)) angles were measured as probe fluid was supplied via a syringeinto or out of sessile droplets (drop volume approximately 5 μL).Measurements were taken at four different spots on each film, and thereported uncertainties are standard deviations associated with theseeight contact angle values (a left-side and right-side measurement foreach drop).

Methodology for Computing Surface Energy Values

While in principle the matrix presented in Equation 8 is solvable usingthe advancing and receding contact angles of just three liquids, smalluncertainties in the measured contact angles associated with the vectoron the right hand side may yield large differences in the computedsurface energy parameters when the system is mathematicallyill-conditioned. See, for example, S. Lee et al., Langmuir, 2008, 24,4817-4826; C. Della Volpe et al., J. Adhes. Sci. Technol., 1998, 12,1141-1180; and T. Bialopiotrowicz, J. Adhes. Sci. Technol., 2009, 23,799-813, each of which is incorporated by reference in its entirety. Theimpact of outlying data points was reduced and the uncertainty minimizedby using the contact angle measurements from all six probe liquids oneach of the test surfaces. Having six data points and just threeunknowns yields an overdetermined set of equations that can be “solved”according to a least squares criterion. However, the three nonpolarliquids have only dispersion interactions (i.e., γ_(lv) ⁺=γ_(lv) ⁻=0),which makes the problem ill-conditioned. The matrix inversion processfor this multi-collinear system introduces significant uncertainty intothe computed surface energy parameters if they are obtained from asimultaneous least squares fit of all of the experimental data. See, forexample, T. Bialopiotrowicz, J. Adhes. Sci. Technol., 2009, 23, 815-825,which is incorporated by reference in its entirety. Instead ofconsidering simultaneously all of the data, an alternative two-stepapproach can be used: (1) calculate the dispersion component of thesolid surface energy γ_(sv,i) ^(d) from the measured nonpolar liquidcontact angles; (2) determine least squares fits of γ_(sv,i) ⁺ andγ_(sv,i) ⁻ from this computed γ_(sv,i) ^(d) and the measured polarliquid contact angles. See, for example, R. J. Good and C. J. Van Oss,In Modern Approaches to Wettability: Theory and Applications; M.Schrader and G. Loeb, Eds.; New York, Plenum, 1992, 1-27, which isincorporated by reference in its entirety. Such an approachadvantageously circumvents the issues with multicollinearity error,incorporates information from all six liquids to minimize the impact ofany one outlying data point, and ultimately yields meaningful values ofγ_(sv,i) ^(d), γ_(sv,i) ⁺, and γ_(sv,i) ⁻.

Coating Adhesion Testing

The adhesion of deposited films to the underlying silicon wafers wasprobed by using a commercially available cross-cut test kit (BYKGardner, Cat. No. 5123) to follow an ASTM standard testing protocol.See, for example, ASTM Standard D3359-09, Test Methods for MeasuringAdhesion by Tape Test, ASTM International, 2010, which has beenincorporated by reference in its entirety. Briefly, thesupplier-provided flexible cutter was used to create a lattice patternof cuts in each test film. These lattices consisted of eleven cuts,spaced 1 mm apart, that were made in two perpendicular directions. Apiece of 25 mm wide semitransparent pressure sensitive tape (PermacelP99) was placed over the grid of cuts and rapidly peeled off of thesurface at an angle of 180°. The coating was visually inspected andclassified between 0B (worst adhesion) and 5B (best adhesion) accordingto ASTM standards.

Results and Discussion

Liquid contact angles are sensitive to the roughness of a surface, andthe well-known Wenzel equation describes the effects of roughness on themost stable apparent contact angle, θ*, exhibited by fully wetted liquiddroplets:

cos θ*=r cos θ  (6)

where the Wenzel roughness r is defined as the ratio of actual surfacearea to projected surface area and θ is the most stable apparent contactangle on a chemically equivalent smooth surface. See, for example, H.Kamusewitz et al., Colloids Surf A, 1999, 156, 271-279; G. Wolansky andA. Marmur, Colloids Surf, A, 1999, 156, 381-388; and A. Marmur and E.Bittoun, Langmuir, 2009, 25, 1277-1281, each of which has beenincorporated by reference in its entirety. The most stable apparentcontact angle, θ*, has been shown to increase with roughness when θ isabove 90°, and decrease with increasing roughness when θ is below 90°.The roughness-induced increase in θ* when θ exceeds 90° does not,however, correlate with increased liquid repellency of fully wettedWenzel-state droplets, because the apparent receding contact angle,θ*_(rec), generally decreases with increasing roughness regardless ofwhether θ_(rec) measured on a smooth surface is above or below the 90°threshold. This roughness-induced decrease in θ*_(rec) leads to anincreased resistance to both drop pull-off (Equation 5) and also to dropsliding when coupled with the roughness-induced increase in the apparentadvancing contact angle, θ*_(adv) (Equation 3). Thus, θ*_(rec) offully-wetted droplets and the liquid repellency of Wenzel surfaces aremaximized when the roughness of a substrate is minimized.

The morphology and roughness of fluorodecyl POSS films prepared in thiswork varied in the same way as others previously described in theliterature, with both smooth and rough topographies resulting from thesame deposition protocol of spin coating a 20 mg/mL solution at 900 rpmfor 30 sec. For example, one prepared “rough” fluorodecyl POSS film ischaracterized by water contact angles of θ_(adv)=134° and θ_(rec)=106°and a root-mean square roughness R_(q)=86 nm while a “smooth”fluorodecyl POSS sample exhibits water contact angles of θ_(adv)=125°and θ_(rec)=112° and R_(q)=5.9 nm. A scanning electron micrograph of therough fluorodecyl POSS film is provided in FIG. 4A. These variations mayarise from interactions between the rate of solvent evaporation and therate of fluorodecyl POSS crystallization as environmental variables suchas temperature and relative humidity fluctuate. Blends comprisingpolymers and fluorodecyl POSS, in contrast, were consistently andreproducibly deposited as smooth films, and a representative scanningelectron micrograph of an 80/20 PMMA/fluorodecyl POSS sample with waterθ_(adv)=124° and θ_(rec)=118° and R_(q)=2.6 nm is provided in FIG. 4B.Similarly smooth spin-coated films were obtained all of the testedblends of fluorodecyl POSS and TECNOFLON, PMMA, PEMA, or PBMA. Promotingthe deposition of smooth coatings is crucial for maximizing the recedingcontact angles of liquid drops and facilitating their removal fromsubstrates by either the sliding (Equation 3) or pull-off mechanism(Equation 5) because receding contact angle, unlike advancing and moststable apparent contact angles, decreases with roughness even whenθ_(rec) measured on a smooth surface is above 90°. See, for example, A.Marmur, Soft Matter, 2006, 2, 12-17; R. E. Johnson, Jr. and R. H.Dettre, Surfactant Sci. Ser., 1993, 49, 1-73; E. Wolfram and R. Faust,In Wetting, Spreading, and Adhesion, London, Academic Press, 1978,213-222; H. Kamusewitz, W. Possart, and D. Paul, Colloid SurfA-Physicochem. Eng. Asp., 1999, 156, 271-279; and S. Kirk et al., PlasmaProcess. Polym., 2010, 7, 107-122, each of which is incorporated byreference in its entirety.

Incorporating polymeric binders to minimize the roughness of fluorodecylPOSS-containing films will maximize liquid repellency only if thechemical moieties located at or near the surface of the compositecoating are those of the fluorodecyl POSS molecules, and not those ofthe higher energy polymers. Measurements of the advancing and recedingcontact angles of the bifunctional polar (γ_(lv) ⁺, γ_(lv) ⁻≥0) liquidswater, ethylene glycol, and dimethyl sulfoxide, as well as the nonpolar(γ_(lv) ⁺, γ_(lv) ⁻=0) liquids diiodomethane, rapeseed oil, andhexadecane, provide a direct evaluation of the liquid wettability and anindirect probe of the surface composition of the polymer/fluorodecylPOSS blends. Representative data that illustrate key trends arepresented in FIGS. 5 and 6, and the complete set of advancing andreceding contact angle measurements on the polymer/fluorodecyl POSSblends, polycarbonate, TEFLON AF-2400, and1H,1H,2H,2H-perfluorodecyltrichlorosilane are provided in Tables 2 and3. The lines connecting the data points on all plots are intended toguide the eye. In FIG. 5A, the solid symbols connote θ_(adv) and thehollow symbols denote θ_(rec). In FIG. 5C, the solid symbols indicateθ_(adv) and the hollow symbols connote θ_(rec). In FIG. 5C, the solidand hollow symbols denote θ_(adv) and θ_(rec), respectively. In FIG. 5D,the dashed line represents θ_(adv)=180° and the area above and to theleft of this curve is not accessible because it is impossible forθ_(rec)>θ_(adv). The lines between data points connect the individualmeasurements, from right to left, in order of increasing fluorodecylPOSS loadings: 0-1-3-5-10-20-30-50 wt %. The red circles indicatemeasurements for the pure fluorodecyl POSS coating.

TABLE 2 Measured advancing contact angles, θ_(adv), of six probe liquidson the 36 test surfaces^(a). Ethylene Dimethyl Diiodo- Rapeseed Hexa-Sample Water Glycol Sulfoxide methane Oil decane PC  87.2 ± 1.3  7.57 ±3.8  60.5 ± 6.0  40.8 ± 4.1 44.2 ± 6.2 24.0 ± 6.7 Fluoroalkylsilane^(b)123.0 ± 1.9 101.7 ± 1.5 109.8 ± 0.6 106.6 ± 2.4 84.2 ± 2.0 78.4 ± 3.1TEFLON AF-2400 125.4 ± 1.1 103.5 ± 1.1 101.3 ± 1.1 104.4 ± 1.7 82.3 ±2.5 69.7 ± 2.1 PMMA  77.3 ± 1.3  65.4 ± 3.0  47.5 ± 3.2  45.8 ± 1.9 29.7± 6.5 16.1 ± 3.0 99/1 PMMA/ 100.4 ± 3.1  68.3 ± 2.1  55.3 ± 3.9  64.9 ±5.4 38.9 ± 5.8 41.5 ± 2.5 Fluorodecyl POSS 97/3 PMMA/ 108.6 ± 0.5  83.3± 5.6  73.2 ± 1.7  93.4 ± 2.1 71.1 ± 4.1 61.3 ± 4.5 Fluorodecyl POSS95/5 PMMA/ 116.6 ± 1.2  93.6 ± 4.4  89.3 ± 2.3  94.6 ± 3.8 69.9 ± 6.166.4 ± 7.4 Fluorodecyl POSS 90/10 PMMA/ 123.5 ± 1.0 105.5 ± 0.4 102.0 ±1.2 102.3 ± 1.4 83.6 ± 3.2 79.8 ± 1.9 Fluorodecyl POSS 80/20 PMMA/ 123.9± 0.3 104.5 ± 0.5 102.5 ± 0.8 102.5 ± 1.4 86.6 ± 1.2 79.9 ± 1.5Fluorodecyl POSS 70/30 PMMA/ 124.0 ± 0.4 105.0 ± 1.1 104.4 ± 0.4 103.6 ±0.8 87.3 ± 1.4 79.0 ± 0.6 Fluorodecyl POSS 50/50 PMMA/ 124.2 ± 1.1 104.7± 1.4 105.4 ± 0.9 104.8 ± 1.5 87.5 ± 2.2 79.4 ± 1.6 Fluorodecyl POSSPEMA  85.5 ± 1.4  65.3 ± 2.6  54.1 ± 2.4  57.4 ± 2.8 38.3 ± 1.7 16.6 ±2.8 99/1 PEMA/  99.7 ± 1.5  71.8 ± 6.0  69.8 ± 1.8  70.6 ± 2.0 53.0 ±2.9 47.5 ± 1.2 Fluorodecyl POSS 97/3 PEMA/ 117.3 ± 0.8  92.9 ± 6.1  94.0± 1.5  85.7 ± 6.3 81.4 ± 0.7 75.4 ± 0.9 Fluorodecyl POSS 95/5 PEMA/122.0 ± 0.6 102.8 ± 3.8 101.5 ± 1.7  98.5 ± 4.9 81.9 ± 2.8 80.6 ± 1.1Fluorodecyl POSS 90/10 PEMA/ 123.1 ± 0.4 107.3 ± 1.3 102.1 ± 1.0 102.4 ±0.7 85.5 ± 1.7 79.5 ± 0.9 Fluorodecyl POSS 80/20 PEMA/ 124.3 ± 0.5 104.6± 1.6 103.0 ± 1.0 103.2 ± 0.8 85.7 ± 3.4 79.6 ± 1.4 Fluorodecyl POSS70/30 PEMA/ 124.7 ± 0.4 104.5 ± 1.8 102.5 ± 1.2 103.4 ± 0.8 56.5 ± 1.977.1 ± 1.8 Fluorodecyl POSS 50/50 PEMA/ 126.4 ± 0.5 106.1 ± 1.2 106.0 ±0.6 104.2 ± 2.1 87.1 ± 1.8 79.3 ± 1.2 Fluorodecyl POSS PBMA  93.7 ± 0.9 71.5 ± 2.1  69.5 ± 1.6  70.8 ± 5.5 41.8 ± 1.7 22.1 ± 3.0 99/1 PBMA/103.0 ± 2.1  75.4 ± 2.1  71.6 ± 1.6  97.3 ± 3.3 49.1 ± 4.9 41.5 ± 1.0Fluorodecyl POSS 97/3 PBMA/ 117.2 ± 1.0  95.9 ± 1.5  94.7 ± 1.3 c 63.2 ±3.8 60.9 ± 3.9 Fluorodecyl POSS 95/5 PBMA/ 122.0 ± 0.4 102.4 ± 2.2 102.6± 0.7 c 81.8 ± 2.1 76.5 ± 2.8 Fluorodecyl POSS ^(a)Reporteduncertainties are standard deviations from eight measured contact anglevalues. ^(b)1H,1H,2H,2H-perfluorodecyltrichlorosilane. ^(c)Measurementof angles was difficult because drops do not advance smoothly. See FIG.7 for details.

TABLE 3 Measured receding contact angles, θ_(rec), of various probeliquids on the 36 test surfaces^(a). Ethylene Dimethyl Diiodo- RapeseedHexa- Sample Water Glycol Sulfoxide methane Oil decane PC  72.3 ± 1.246.9 ± 4.1 30.1 ± 3.5 15.3 ± 1.9 21.3 ± 2.0 <10 Fluoroalkylsilane^(b) 93.0 ± 3.1 74.5 ± 3.6 66.2 ± 1.4 73.2 ± 2.7 48.9 ± 3.5 53.1 ± 2.1TEFLON AF-2400 113.4 ± 0.8 93.9 ± 2.2 89.3 ± 1.0 88.4 ± 2.3 58.6 ± 3.758.1 ± 2.8 PMMA  61.2 ± 1.4 43.0 ± 3.0 31.2 ± 3.0 22.2 ± 1.3 15.3 ± 2.3<10 99/1 PMMA/  63.9 ± 1.0 48.7 ± 2.0 31.3 ± 2.1 23.5 ± 3.3 15.8 ± 1.316.1 ± 2.3 Fluorodecyl POSS 97/3 PMMA/  74.7 ± 1.2 52.9 ± 3.8 33.0 ± 5.226.3 ± 2.8 30.1 ± 5.0 22.5 ± 2.8 Fluorodecyl POSS 95/5 PMMA/  91.2 ± 2.067.4 ± 3.5 36.6 ± 3.4 35.0 ± 3.5 34.4 ± 3.6 31.6 ± 5.9 Fluorodecyl POSS90/10 PMMA/ 115.2 ± 0.8 92.1 ± 1.8 54.4 ± 1.8 68.8 ± 8.6 49.8 ± 6.0 46.2± 5.8 Fluorodecyl POSS 80/20 PMMA/ 118.1 ± 0.8 99.2 ± 0.8 84.6 ± 0.888.2 ± 2.7 79.0 ± 1.8 74.6 ± 2.0 Fluorodecyl POSS 70/30 PMMA/ 119.8 ±0.8 98.4 ± 1.8 89.0 ± 1.1 87.4 ± 3.0 75.8 ± 3.5 73.4 ± 2.9 FluorodecylPOSS 50/50 PMMA/ 118.3 ± 1.9 97.8 ± 3.1 90.7 ± 1.0 90.8 ± 4.0 78.4 ± 1.473.1 ± 0.9 Fluorodecyl POSS PEMA  70.5 ± 1.9 52.4 ± 2.7 38.8 ± 1.5 19.5± 4.1 17.5 ± 1.2 <10 99/1 PEMA/  75.9 ± 1.0 53.4 ± 2.5 39.4 ± 2.5 23.2 ±2.5 28.0 ± 2.8 19.9 ± 2.2 Fluorodecyl POSS 97/3 PEMA/  98.0 ± 2.0 65.1 ±3.4 47.8 ± 4.0 34.4 ± 3.7 46.4 ± 7.0 21.4 ± 2.1 Fluorodecyl POSS 95/5PEMA/ 112.7 ± 2.4 75.1 ± 8.8 65.8 ± 4.6 44.3 ± 7.6 55.2 ± 12.3 51.5 ±6.2 Fluorodecyl POSS 90/10 PEMA/ 119.3 ± 1.7 90.3 ± 3.3 84.9 ± 1.8 77.8± 4.1 70.2 ± 4.7 73.9 ± 1.6 Fluorodecyl POSS 80/20 PEMA/ 117.9 ± 2.198.3 ± 2.3 88.3 ± 1.0 91.8 ± 2.5 77.7 ± 1.3 73.3 ± 1.6 Fluorodecyl POSS70/30 PEMA/ 117.7 ± 1.3 98.0 ± 2.5 87.1 ± 2.1 83.3 ± 1.8 78.8 ± 0.6 71.3± 3.7 Fluorodecyl POSS 50/50 PEMA/ 117.8 ± 0.5 96.1 ± 2.0 91.8 ± 1.086.4 ± 1.4 75.7 ± 1.9 70.7 ± 2.1 Fluorodecyl POSS PBMA  77.7 ± 0.8 59.7± 1.0 58.2 ± 1.5 25.7 ± 6.4 18.0 ± 1.8 13.4 ± 2.3 99/1 PBMA/  79.9 ± 2.066.8 ± 2.3 53.1 ± 2.4 23.5 ± 4.9 25.7 ± 5.1 23.2 ± 2.7 Fluorodecyl POSS97/3 PBMA/  99.5 ± 1.6 82.0 ± 2.7 69.5 ± 1.0 34.1 ± 4.8 26.5 ± 6.7 36.1± 2.7 Fluorodecyl POSS 95/5 PBMA/ 116.4 ± 1.4 90.7 ± 5.0 77.8 ± 3.2 35.1 ± 11.2 43.8 ± 5.8 40.9 ± 5.7 Fluorodecyl POSS ^(a)Reporteduncertainties are standard deviations from eight measured contact anglevalues. ^(b)1H,1H,2H,2H-perfluorodecyltrichlorosilane.

Water contact angle measurements for all of the testedpolymer/fluorodecyl POSS materials are presented graphically in FIG. 5A.The advancing water contact angle increased rapidly as fluorodecyl POSSis added to each of the pure polymers, reaching θ_(adv)=124±4° atfluorodecyl POSS loadings of 10 wt % and above (f_(POSS)≥0.10). Thereceding water contact angles also increased as fluorodecyl POSS isadded to the polymers, but they plateaued at different values fordifferent polymeric binders. For PMMA, PEMA, and PBMA, θ_(rec) reaches118±2° for f_(POSS)≥0.20, while for the TECNOFLON-containing blendsθ_(rec) increased more slowly as fluorodecyl POSS was added and onlyreaches 114±1° when f_(POSS)=0.50. Comparable maximum values in θ_(adv)and different plateaus in θ_(rec) were similarly obtained for the otherpolar probe fluids ethylene glycol and dimethyl sulfoxide on the testsurfaces, as illustrated in FIGS. 5B and 5C. The data for the PEMA andPBMA materials essentially tracked those for the PMMA blends and wereomitted from these plots to maximize clarity.

An alternative means of presenting these wettability data is to considerthe sliding and pull-off mechanisms described by Equations 3 and 5,respectively. The two dimensionless solid-liquid interaction parametersthat scale with the ease of drop removal by these processes are S_(α)for drop sliding (Equation 3) and the quantity (1+cos θ_(rec)) for droppull-off (Equation 5). A plot of S_(α) versus (1+cos θ_(rec)) thusrepresents graphically the changes in the relative importance of thesetwo physical processes. Data on this wettability plot must lie below andto the right of a curve that represents the limiting value θ_(adv)=180°because it is not possible for θ_(rec) to exceed θ_(adv). The resistanceto drop sliding increases monotonically as S_(α) increases, with datapoints on the abscissa (θ_(adv)=θ_(rec), S_(α)=0) indicative of dropsthat will slide or roll at any angle of tilt regardless of themagnitudes of θ_(adv) and θ_(rec). The ease of drop sliding is not acomplete description of liquid wettability, however, because it does notrelate directly to the practical work of adhesion required to pull aliquid drop vertically off of a substrate. This pull-off work scaleswith the parameter (1+cos θ_(rec)) and increases monotonically with thedistance along the abscissa. The most liquid-repellent substrates arecharacterized by both facile drop sliding (low ordinate value) and droppull-off (low abscissa value), and are represented on this wettabilitydiagram by the points nearest the origin.

The data for the bifunctional polar liquids water and dimethyl sulfoxideon TECNOFLON/fluorodecyl POSS blends and representative PMMA/fluorodecylPOSS materials are presented in this form in FIG. 5D. Ethylene glycoldata for these surfaces substantially overlapped with the correspondingdimethyl sulfoxide curves and were omitted from this diagram to maximizeclarity. The curves for the polar liquid droplets on the PMMA blends gotcloser to the origin than those for the TECNOFLON materials,illustrating the enhanced repellency to such liquids for thepolymethacrylate blends. The optimal polymethacrylate/fluorodecyl POSSsamples were in fact more liquid repellent than a spin-cast purefluorodecyl POSS film (FIG. 6D), likely due to the smoother surfacetopography, and consequent higher receding contact angles, of thepolymer/fluorodecyl POSS blends, as discussed earlier.

In FIG. 6A, the solid symbols denoted θ_(adv) and the hollow symbolsrepresent θ_(rec). Stable values of θ_(adv) were difficult to ascertainfor the PBMA-based materials with 0.03≤f_(POSS)≤0.30. In FIG. 6B, thesolid and hollow symbols represent θ_(adv) and θ_(rec), respectively. InFIG. 6C, the solid and hollow symbols connote θ_(adv) and θ_(rec),respectively. In FIG. 6D, the points nearest the origin corresponded tothe most liquid repellent substrates. The dashed line representedθ_(adv)=180° and the area above and to the left of this curve was notaccessible because it is impossible for θ_(rec) to exceed θ_(adv). Thelines between data points connect the individual measurements, fromright to left, in order of increasing fluorodecyl POSS loadings:0-1-3-5-10-20-30-50 wt %. The circles represented measurements for thepure fluorodecyl POSS film. In this plot, the minimum observed advancingangle of 95 ° was assigned as θ_(adv) for diiodomethane drops on thePBMA blends with 0.03≤f_(POSS)≤0.30. If any of the larger anglesobserved during diiodomethane drop advancing were used as θ_(adv), S_(α)would be even higher, meaning our choice represented the maximumpossible diiodomethane repellency for the PBMA materials.

A complete assessment of the liquid wettability of a substrate requiredinformation about the behavior of both polar and nonpolar liquids thatcontact the surface. To probe the behavior of nonpolar liquids,advancing and receding contact angles of diiodomethane, rapeseed oil,and hexadecane were also measured on all of the test substrates. Theadvancing and receding contact angle values for diiodomethane on each ofthe polymer/fluorodecyl POSS test materials were plotted as a functionof the fluorodecyl POSS loading in FIG. 6A. Stable advancing angles fordiiodomethane on the PBMA blends with 0.03≤f_(POSS)≤0.30 were difficultto measure, as illustrated in FIG. 7, and consequently were not includedin FIG. 6A. Similar to the advancing contact angle data presented inFIG. 5, the diiodomethane advancing contact angles increased rapidly asfluorodecyl POSS is added to the pure polymers and reach an asymptoticlimit of θ_(adv)=104±3° for f_(POSS)≥0.10. The receding contact anglesalso increase with the addition of fluorodecyl POSS and level off atθ_(rec)=88±4° when f_(POSS)≥0.20 for the PMMA, PEMA, and TECNOFLONblends. Receding contact angle measurements for diiodomethane drops onthe PBMA materials, however, remained below this plateau, much like thepolar liquid receding contact angle values did on the TECNOFLON blendsin FIG. 5. In contrast to the diiodomethane behavior, the trends inreceding contact angle for two other nonpolar liquids, rapeseed oil andhexadecane, were not substantially different for the PBMA-basedmaterials and the other polymer/fluorodecyl POSS blends, as illustratedin FIGS. 6B and 6C. The contact angle data for the TECNOFLON/fluorodecylPOSS and PEMA/fluorodecyl POSS materials followed the same trends as thePMMA/fluorodecyl POSS measurements and were omitted from these plots tomaximize clarity.

Using the wettability diagram representation discussed above, thenonpolar liquid contact angle data for diiodomethane and hexadecane onthe representative PMMA materials and outlying PBMA blends werereplotted in FIG. 6D. The rapeseed oil data overlapped significantlywith the hexadecane measurements and were excluded from this diagram tomaximize clarity. The termination of the hexadecane (and omittedrapeseed oil) curves at essentially the same spot for both sets ofmaterials illustrated that the maximum liquid repellency of these twoliquids was similar on the PBMA-based and PMMA-based samples. Incontrast, the curve for droplets of diiodomethane with γ_(lv)=50.8 mN/mterminated closer to the origin for the PMMA materials than it does forthe PBMA blends, illustrating that the diiodomethane repellency washigher for the optimal PMMA samples than for the best PBMA blend. As inFIG. 5, the optimal polymer/fluorodecyl POSS blends were even moreliquid repellent than pure fluorodecyl POSS (FIG. 6D), most likely dueto the increased roughness of the pure fluorodecyl POSS film.

The detailed shapes of the curves in FIGS. 5D and 6D merit somediscussion. The solid lines in the diagrams guide the eye by connectingthe data points in the order of increasing fluorodecyl POSS content inthe films. The wettability parameter (1+cos θ_(rec)) decreasedmonotonically as the fluorodecyl POSS loading increased, with oneexception: the pure fluorodecyl POSS films exhibited higher (1+cosθ_(rec)) values than the PMMA blends with fluorodecyl POSS loadings of20 wt % and above. This slight decrease in θ_(rec) for the purefluorodecyl POSS coatings may have been caused by subtle surfaceroughness effects in the pure films. In contrast to the quantity (1+cosθ_(rec)), the sliding parameter, S_(α), was not monotonic; it initiallyincreased at low fluorodecyl POSS loadings, peaked, and then decreasedtowards an asymptotic minimum value. The initial rise in S_(α) wasdriven by an increase in contact angle hysteresis that resulted fromθ_(adv) increasing more rapidly than θ_(rec) as fluorodecyl POSS wasadded to the neat polymers. The subsequent decrease in S_(α) occurred asθ_(adv) reached a plateau while θ_(rec) continued to increase towardsits asymptotic maximum value, which minimized the hysteresis. Theunequal rates of change in θ_(adv) and θ_(rec) were likely driven bydifferent sensitivities of contact line pinning to the multiplecomponents of a chemically heterogeneous surface. The advancing contactline was most sensitive to the low energy portion of the surface andincreased rapidly as fluorodecyl POSS began to occupy a significantfraction of the surface. The receding contact line, in contrast, wasmost sensitive to the high energy components of the surface (i.e., thepolymer rich domains), and did not increase substantially until thefluorodecyl POSS domains covered nearly all of the surface.

In general, pinning of the receding contact line and contact anglehysteresis are sensitive to three surface properties: roughness,chemical heterogeneity, and molecular rearrangements in the solidsubphase. See, for example, C. W. Extrand, In Encyclopedia of Colloidand Surface Science, Vol. 4; P. Somasundaran, Ed.; Boca Raton, Fla., CRCPress, 2006, 2876-2891, which is incorporated by reference in itsentirety. Systematic differences in one or more of these surfaceattributes were likely responsible for the sensitivity of recedingcontact angle measurements for diiodomethane and polar liquid drops tothe identity of the polymeric binder for the materials withf_(POSS)≥0.20. The contact angle data did not vary systematically withvariations in roughness for the different polymeric binders, as only thepolar liquids and diiodomethane exhibited a dependence of θ_(rec) theidentity of the polymer. The variations in liquid wettability for thedifferent blend series must therefore be driven by specific interactionsbetween certain contacting liquids and the blend surfaces. XPS wasdeployed to examine possible differences in chemical heterogeneity byprobing the chemical composition of the top 10 nm of films of 80/20TECNOFLON/fluorodecyl POSS and 80/20 PEMA/fluorodecyl POSS. See, forexample, Y. Mao and K. K. Gleason, Macromolecules, 2006, 39, 3895-3900and D. L. Schmidt et al., Nature, 1994, 368, 39-41, each of which hasbeen incorporated by reference in its entirety. These XPS survey andhigh resolution carbon is spectra are provided in FIG. 8. The atomicratios calculated from these raw data are provided in Table 4 along withthose expected for pure fluorodecyl POSS. The values for the two testsurfaces were essentially identical, and very close to those expectedfor pure fluorodecyl POSS. These results were consistent with thefluorodecyl POSS molecules blooming up and minimizing chemicalheterogeneity by covering nearly the entire surface of each blend.

TABLE 4 Measured atomic ratios at the surfaces of 80/20TECNOFLON/fluorodecyl POSS and 80/20 PEMA/fluorodecyl POSS materials andcalculated atomic ratios for pure fluorodecyl POSS. Sample F/C O/C Si/C80/20 TECNOFLON/ 1.52^(a) 0.11^(a) 0.08^(a) Fluorodecyl POSS 80/20 PEMB/1.54^(a) 0.11^(a) 0.09^(a) Fluorodecyl POSS Fluorodecyl POSS 1.7^(b)0.15^(b) 0.1^(b) ^(a)Determined using XPS survey spectra. ^(b)Calculatedvalues.

The surface composition of each polymer/fluorodecyl POSS blend can alsobe altered by molecular rearrangement that is induced by contact withthe probe fluid. See, for example, C. W. Extrand, In Encyclopedia ofColloid and Surface Science, Vol. 4; P. Somasundaran, Ed.; Boca Raton,Fla., CRC Press, 2006, 2876-2891, which is incorporated by reference inits entirety. Such reorientations lower the total free energy of thethree phase system by increasing favorable interactions between theliquid and the underlying substrate and consequently reducing θ_(rec).See, for example, Y. Mao and K. K. Gleason, Macromolecules, 2006, 39,3895-3900, which is incorporated by reference in its entirety. Suchsurface rearrangements may be responsible for the systematically lowerreceding contact angle values measured for polar liquids onTECNOFLON/fluorodecyl POSS blends and for diiodomethane drops onPBMA/fluorodecyl POSS materials. Both TECNOFLON and PMBA containsegments that are rubbery and mobile at room temperature, as evidencedby the measured glass transition temperatures of −9° C. for TECNOFLONand 10° C. for PBMA. The acidic —CF₂—CH₂— protons in TECNOFLON and thedispersive alkyl segments in PBMA can reorient to enhance favorableinteractions with the appropriate contacting liquids. See, for example,S. Lee, J. S. Park, and T. R. Lee, Langmuir, 2008, 24, 4817-4826, whichis incorporated by reference in its entirety. The glassy PMMA(T_(g)=124° C.) and PEMA (T_(g)=77° C.) segments do not, in contrast,possess sufficient mobility at room temperature to quickly reorient.

The advancing and receding contact angle measurements for all six testliquids can be used in conjunction with the matrix formulation providedin Equation 8 and the protocol described in the Examples to calculatethe dispersion (γ_(sv,i) ^(d)), acidic (γ_(sv,i) ⁺), and basic (γ_(sv,i)⁻) components of the advancing and receding solid surface energy values,γ_(sv,α) and γ_(sv,r). Advancing contact angle data for diiodomethane onthe PBMA blends with 0.03≤f_(POSS)≤0.30 are not used in thesecalculations because the drops advanced by a slip/stick mechanism,making the measurements unreliable for surface energy analysis. See, forexample, D. Y. Kwok and A. W. Neumann, Adv. Colloid Interface Sci.,1999, 81, 167-249, which is incorporated by reference in its entirety.The surface energy values for all of our test materials are provided inTable 5. Notably the fluorodecyl POSS materials were distinguishablefrom fluorinated alternatives such as TEFLON AF-2400 and1H,1H,2H,2H-perfluorodecyltrichlorosilane (fluoroalkylsilane), which iswidely used by the surface science community to reduce the liquidwettability of substrates. The key differences amongst these fluorinatedmaterials did not appear in the often-considered advancing surfaceenergy values, γ_(sv,α) ^(d), which were comparable. Rather it was thereceding surface energy values, γ_(sv,r) that were noticeably higher forTEFLON AF-2400 and the fluoroalkylsilane than they were for theoptimized fluorodecyl POSS-containing samples. It was the low recedingsurface energy values that minimize the resistance to both drop slidingand drop pull-off and distinguished fluorodecyl POSS as a stronglyliquid repellent material.

Surface energy terms for selected representative test samples wereplotted in FIG. 9 to examine the trends when fluorodecyl POSS is blendedwith the various polymers. Solid symbols denote advancing values whilehollow symbols indicate receding terms. FIG. 9A shows the variation inthe overall advancing and receding surface energy values, γ_(sv,α) andγ_(sv,r), for the PMMA/fluorodecyl POSS and PBMA/fluorodecyl POSS blendsas a function of the fluorodecyl POSS loading. The advancing surfaceenergy values for both sets of materials decreased sharply asfluorodecyl POSS was blended with the pure polymers and reach a minimumvalue of γ_(sv)≈9±1 mN/m for fluorodecyl POSS loadings of 10 wt % andabove. The receding surface energy values of these two series of blendsdiffered significantly, however, due to the marked differences inreceding contact angles of diiodomethane drops. For the PMMA materials,γ_(sv,r) declined as fluorodecyl POSS was added and reached a minimum ofγ_(sv,r)=13±1 mN/m for f_(POSS)≥0.20. The values of the receding surfaceenergy values for the PBMA materials also decreased as fluorodecyl POSSwas added, but did so to much less of an extent than they did for thePMMA blends and only reached a minimum value of 16 mN/m for /Foss=0.50.These elevated values of γ_(sv,r) for PBMA surfaces were the result oflarger dispersion interactions, γ_(sv,r) ^(d). This increase in γ_(sv,r)^(d) may have been driven by molecular rearrangements in the moreleathery PBMA materials that enable favorable interactions betweendiiodomethane and the polymer chains. Similar molecular reorientationswere not prevalent in the glassy PMMA (T_(g)=124° C.) and PEMA(T_(g)=77° C.) materials because the polymer chains did not possesssufficient mobility for rapid rearrangement.

TABLE 5 Values of total (γ_(sv,i)), dispersion (γ_(sv,r) ^(d)), polar(γ_(sv,r) ^(d)), hydrogen bond donating (γ_(sv,r) ^(d)), and hydrogenbond accepting (γ_(sv,r) ^(d)) surface energy values calculated fromadvancing and receding contact angles^(a). Surface Energy Values SurfaceEnergy Values from Advancing from Receding Contact Angles Contact Angles(mN/m) (nm/m) Sample γ_(sv,a) γ_(sv,a) ^(d) γ_(sv,a) ^(p) γ_(sv,a) ⁺γ_(sv,a) ⁻ γ_(sv,r) γ_(sv,r) ^(d) γ_(sv,r) ^(p) γ_(sv,r) ⁺ γ_(sv,r) ⁻TEFLON AF-2400 9.6 9.6 0.001 0.01 0.03 16.6 16.1 0.42 0.05 0.82Fluoroalkylsilane 8.6 8.5 0.10 0.01 0.53 22.7 21.2 1.5 0.11 5.1 PC 39.335.2 4.1 0.23 18.4 40.4 38.3 2.1 0.10 11.4 PMMA 33.1 32.3 0.88 0.01 13.339.6 37.9 1.7 0.03 23.1 99/1 PMMA/ 26.1 25.3 0.81 0.51 0.33 38.4 37.40.97 0.01 21.2 Fluorodecyl POSS 97/3 PMMA/ 14.5 13.4 1.1 0.95 0.30 37.735.6 2.1 0.10 10.7 Fluorodecyl POSS 95/5 PMMA/ 13.2 13.0 0.21 0.05 0.2234.1 33.2 0.91 0.11 1.9 Fluorodecyl POSS 90/10 PMMA/ 9.2 9.2 0.04 0.010.25 23.3 22.7 0.53 0.14 0.050 Fluorodecyl POSS 80/20 PMMA/ 8.9 8.9 0.040.00 0.19 12.7 12.6 0.14 0.06 0.08 Fluorodecyl POSS 70/30 PMMA/ 8.7 8.70.01 0.00 0.26 13.3 13.2 0.03 0.01 0.04 Fluorodecyl POSS 50/50 PMMA/ 8.58.5 0.00 0.00 0.26 12.4 12.3 0.12 0.02 0.20 Fluorodecyl POSS PEMA 29.728.6 1.1 0.004 7.0 38.6 38.1 0.53 0.01 15.9 99/1 PEMA/ 22.9 21.8 1.10.18 1.7 37.3 36.4 0.94 0.02 10.6 Fluorodecyl POSS 97/3 PEMA/ 12.9 12.80.14 0.02 0.27 32.9 32.5 0.44 0.15 0.33 Fluorodecyl POSS 95/5 PEMA/ 10.09.9 0.07 0.01 0.33 27.5 27.2 0.28 0.006 0.33 Fluorodecyl POSS 90/10PEMA/ 9.1 9.0 0.12 0.01 0.38 15.9 15.8 0.09 0.06 0.04 Fluorodecyl POSS80/20 PEMA/ 8.9 8.9 0.02 0.00 0.16 12.3 12.1 0.21 0.03 0.32 FluorodecylPOSS 70/30 PEMA/ 8.9 8.9* 0.04 0.01 0.11 13.9 13.9 0.03 0.00 0.15Fluorodecyl POSS 50/50 PEMA/ 8.6 8.6 0.03 0.01 0.10 13.7 13.6 0.02 0.000.24 Fluorodecyl POSS PBMA 25.4 25.3 0.12 0.00 4.7 41.2 37.0 4.3 0.3314.0 99/1 PBMA/ 18.8 17.3 1.5 0.59 1.0 41.2 37.0 4.3 0.39 12.2Fluorodecyl POSS 97/3 PBMA/ 17.7 17.0 0.70 0.27 0.46 37.2 33.8 3.4 1.02.8 Fluorodecyl POSS 95/5 PBMA/ 11.2 11.1 0.16 0.04 0.17 31.5 31.4 0.121.1 0.01 Fluorodecyl POSS 90/10 PBMA/ 10.9 10.5 0.39 0.07 0.52 29.0 28.70.32 0.99 0.03 Fluorodecyl POSS 80/20 PBMA/ 10.2 9.8 0.38 0.06 0.59 23.623.5 0.10 0.40 0.01 Fluorodecyl POSS 70/30 PBMA/ 10.3 10.2 0.13 0.030.13 22.4 21.6 0.83 0.68 0.25 Fluorodecyl POSS 50/50 PBMA/ 8.5 8.5 0.010.00 0.01 16.1 16.0 0.10 0.02 0.15 Fluorodecyl POSS TECNOFLON 11.6 11.40.22 0.05 0.23 32.1 28.0 4.1 0.39 10.8 99/1 PBMA/ 6.5 6.1 0.42 0.06 0.7825.4 19.8 5.6 1.2 6.6 Fluorodecyl POSS 97/3 PBMA/ 7.3 7.0 0.27 0.03 0.5721.7 16.6 5.1 1.3 4.8 Fluorodecyl POSS 95/5 PBMA/ 8.1 8.0 0.06 0.01 0.3018.6 15.1 3.5 0.65 4.9 Fluorodecyl POSS 90/10 PBMA/ 8.0 7.9 0.14 0.010.45 17.4 14.7 2.7 0.44 4.3 Fluorodecyl POSS 80/20 PBMA/ 7.8 7.8 0.010.00 0.36 14.5 12.8 1.7 0.60 1.2 Fluorodecyl POSS 70/30 PBMA/ 8.5 8.40.11 0.02 0.19 13.6 12.8 0.79 0.41 0.38 Fluorodecyl POSS 50/50 PBMA/ 8.28.1 0.04 0.01 0.06 13.6 13.4 0.25 0.55 0.03 Fluorodecyl POSS FluorodecylPOSS 8.0 7.9 0.02 0.00 0.18 14.5 13.9 0.60 0.23 0.38 ^(a)Considerationof a typical error in contact angle measurement (Δθ≈2°) and thecondition number of the transformation matrix in the system of linearequations yields an approximately 15% relative error in the calculatedsurface energy values. ^(b)1H,1H,2H,2H-Perfluorodecyltrichlorosilane.^(c)Advancing contact angles of diiodomethane drops on PBMA blends with0.01 ≤ ƒ_(POSS) ≤ 0.30 were difficult to measure (see FIG. 7) and werenot used to calculate the advancing surface energy terms for thesematerials.

The advancing and receding surface energy values of PMMA/fluorodecylPOSS and TECNOFLON/fluorodecyl POSS materials were plotted as a functionof the fluorodecyl POSS loading in FIG. 9B. For both sets of materials,γ_(sv,α) and γ_(sv,r) decreased as the fluorodecyl POSS loadings wereincreased and reach plateaus of γ_(sv,α)=8±2 mN for f_(POSS)≥0.10 andγ_(sv,r)=13±2 mN for f_(POSS)≥0.20. Despite the similar values ofγ_(sv,r), for samples with f_(POSS)≥0.20, the receding contact angles ofpolar liquids were consistently lower on the TECNOFLON materials than onthe PMMA blends, as was shown in FIG. 5. Understanding the energeticcharacteristics that drive this difference in polar liquid wettabilityrequired a closer examination of the subcomponents of γ_(sv,r).

The polar contributions to the receding surface energy γ_(sv,r) ^(p),were plotted as a function of fluorodecyl POSS content for thePMMA-based and TECNOFLON-based materials in FIG. 9C. In contrast to thecalculated values shown in FIG. 9B, here there was a clear differencebetween these two data sets, with the polar contribution γ_(sv,r) ^(p)always lower for the PMMA surfaces than for the TECNOFLON substrates.Such a result was consistent with the lower receding contact angles thatwere measured for droplets of polar liquids on the TECNOFLON-containingmaterials as compared to the PMMA samples (see FIG. 5 or Table 3).However, the monotonic decrease in γ_(sv,r) ^(p) for theTECNOFLON/fluorodecyl POSS samples with increasing fluorodecyl POSScontent did not correlate with the measured values of receding contactangles for ethylene glycol and dimethyl sulfoxide drops. Neither ofthese liquids exhibited values of θ_(rec) that increase as γ_(sv,r) ^(p)decreases. Rather, both fluids establish statistically-indistinguishablevalues of the receding contact angle θ_(rec) on all of theTECNOFLON-based samples with at least 20 wt % fluorodecyl POSS.

The polar contribution to the receding surface energy, γ_(sv,r) ^(p),did not correlate with the measured values of the receding contactangles for ethylene glycol and dimethyl sulfoxide because γ_(sv,r) ^(p)is a function of the product of the acidic and basic contributions tothe solid surface energy, γ_(sv,r) ⁺ and γ_(sv,r) ⁻, respectively, asdefined in Equation 6. Liquid contact angles were not, however,sensitive to this product of solid surface parameters, but ratherdepended on the complementary acid/base interactions between the solidand the contacting fluid, as demonstrated in Equation 7. Thus it is thecross products √{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)} and √{squareroot over (γ_(sv,r) ⁻γ_(lv) ⁺)}, and not γ_(sv,r) ^(p) that influencereceding liquid contact angles. For our analysis, we selected the widelyused, albeit arbitrary, reference state in which water is characterizedby equivalent acidic and basic components such that γ_(lv) ⁺=γ_(lv)⁻=25.5 mN/m. Most polar liquids other than water, including the ethyleneglycol and dimethyl sulfoxide used in this work, are characterized asbasic (i.e., high values of γ_(lv) ⁻) when this reference state is used.The wettability of these more basic liquids is sensitive to thecomplementary acidic component of the solid surface energy, γ_(sv,r) ⁺,and the magnitude of such contributions can be examined by computing thecomponents of the practical work of adhesion (Equation 7). These valueswere provided in Table 6 for the representative interactions betweenethylene glycol and four different test surfaces, along with themeasured values of the receding contact angle, θ_(rec), for ethyleneglycol. The substantial difference in the interactions between ethyleneglycol (and other basic liquids) and these two sets of surfaces was thatthe √{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)} contribution wassignificantly higher for the TECNOFLON blends than it was for the PMMAmaterials. The solid surface characteristic responsible for this√{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)} interaction was the termγ_(sv,r) ⁺, and this latter parameter was plotted as a function offluorodecyl POSS loading for the PMMA and TECNOFLON materials in FIG.9D. The γ_(sv,r) ⁺ values reached a plateau for both sample sets oncethe fluorodecyl POSS loading reached 20 wt %, with the TECNOFLONγ_(sv,r) ⁺ plateau well above its PMMA counterpart.

These differences in the acidic component of the solid surface energy,γ_(sv,r) ⁺ may reduce receding contact angles for basic liquids onTECNOFLON/fluorodecyl POSS samples with f_(POSS)≥0.20 below the valuesexhibited by the same fluids on PMMA blends with comparablecompositions. Furthermore, the invariance in both γ_(sv,r) ⁺ andγ_(sv,r) ^(d) for f_(POSS)≥0.20 was consistent with the plateaus inpolar liquid θ_(rec) that were reported in Table 3. This consistencywith all aspects of the experimental liquid contact angle trends madeγ_(sv,r) ⁺ (or γ_(sv,r) ⁻ for acidic liquids) a more relevant parameterthan γ_(sv,r) ^(p) in the assessment of the liquid wettability of asurface. In general, consideration of the total polar contribution tothe solid surface energy, γ_(sv,r) ^(p), was of limited utility forseveral reasons. First,

$\gamma_{{sv},r}^{p} = \sqrt{\gamma_{{sv},r}^{+}\gamma_{{sv},r}^{-}}$

is the product of the individual acidic and basic energeticcharacteristics of the solid surface itself. The solid surface is notinteracting with itself, however, but rather with contacting liquids,and it is the cross products √{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)}and √{square root over (γ_(sv,r) ⁻γ_(lv) ⁺)} that influence liquidwettability. Second, the polar contribution to the surface energy,γ_(sv,r) ^(p), can have a small magnitude that makes it appearnegligible relative to γ_(sv,r) ^(d) when either γ_(sv,r) ⁺ or γ_(sv,r)⁻ is near zero. This apparently low contribution of polar terms can leadto the erroneous conclusion that polar liquids do not interactspecifically with a surface. For example, the 50/50TECNOFLON/fluorodecyl POSS and 50/50 PEMA/fluorodecyl POSS samples werecharacterized by comparable values of the total receding surface energy,γ_(sv,r), and for both materials the polar contributions, γ_(sv,r) ^(p),were less than 2% of γ_(sv,r). However, these similarities in γ_(sv,r)and γ_(sv,r) ^(p) did not lead to comparable repellency for basicliquids. The receding contact angles of both dimethyl sulfoxide andethylene glycol were higher on 50/50 PEMA/fluorodecyl POSS than theywere on 50/50 TECNOFLON/fluorodecyl POSS. These differences in θ_(rec)can only be rationalized when γ_(sv,r) ⁺ (or γ_(sv,r) ⁻ for acidicliquids), γ_(sv,r) ^(d) and, by extension, the three subcomponents ofthe practical work of adhesion (√{square root over (γ_(sv,r) ^(d)γ_(lv)^(d))}, √{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)}, and √{square root over(γ_(sv,r) ⁺γ_(lv) ⁻)}) were evaluated.

TABLE 6 Ethylene glycol receding contact angles and values of thecontributions to the practical work of adhesion, W_(P), for ethyleneglycol on 80/20 PMMA/fluorodecyl POSS, 50/50 PMMA/fluorodecyl POSS,80/20 TECNOFLON/fluorodecyl POSS, and 50/50 TECNOFLON/fluorodecyl POSS.Absolute Magnitudes (mN/m) Fraction of Wp Sample Ethylene Glycol θ_(rec)$\sqrt{\gamma_{{sv},r}^{d}\gamma_{lv}^{d}}$$\sqrt{\gamma_{{sv},r}^{+}\gamma_{lv}^{-}}$$\sqrt{\gamma_{{sv},r}^{-}\gamma_{lv}^{+}}$$\sqrt{\gamma_{{sv},r}^{d}\gamma_{lv}^{d}}$$\sqrt{\gamma_{{sv},r}^{+}\gamma_{lv}^{-}}$$\sqrt{\gamma_{{sv},r}^{-}\gamma_{lv}^{+}}$ 80/20 PMMA/ 99.2 ± 0.8 19.01.7 0.1 0.91 0.08 0.01 Fluorodecyl POSS 50/50 PMMA/ 97.8 ± 3.1 18.8 0.90.6 0.92 0.05 0.03 Fluorodecyl POSS 80/20 85.5 ± 2.1 19.1 5.3 1.5 0.740.21 0.05 TECNOFLON/ Fluorodecyl POSS 50/50 86.5 ± 1.6 19.6 5.1 0.2 0.790.20 0.01 TECNOFLON/ Fluorodecyl POSS

The most liquid-repellent fluorodecyl POSS-containing materials studiedherein were the PMMA/fluorodecyl POSS and PEMA/fluorodecyl POSS blendswith fluorodecyl POSS loadings of 20 wt % and above. These blends weregenerally even more liquid repellent than pure fluorodecyl POSS coatingsbecause the addition of a polymeric binder facilitated the deposition ofsmooth films that minimize contact line pinning and liquid adhesion.There were numerous other benefits to mixing polymers with fluorodecylPOSS besides reducing coating roughness. First, as a result of surfacesegregation, only about 20 wt % fluorodecyl POSS was required tomaximize liquid repellency. The PMMA and PEMA matrix polymers aresignificantly cheaper than the fluorodecyl POSS and widely availablecommercially, reducing the cost of liquid repellent fluorodecylPOSS-based coatings. Furthermore, the polymer/fluorodecyl POSS blendswere optically transparent, as illustrated in FIG. 10A. Pure fluorodecylPOSS coatings, on the other hand, were white powder that hinderstransmission of visible light, as illustrated in FIG. 10B. Finally,cross-cut tape adhesion tests revealed that the PMMA/fluorodecyl POSSand PEMA/fluorodecyl POSS blends adhered significantly more strongly tothe underlying substrates than either the TECNOFLON/fluorodecyl POSS orpure fluorodecyl POSS coatings. Large sections of an 80/20TECNOFLON/fluorodecyl POSS blend (ASTM-categorized adhesion strength of1 B) and pure fluorodecyl POSS coating (3 B) were removed from coatedsilicon wafers during the test while an 80/20 PEMA/fluorodecyl POSS filmremains adhered to the underlying substrate (5 B). FIGS. 11A and 11Bshows photographs of silicon wafers coated with the 80/20 blends andsubjected to the cross-cut adhesion test. The high surface energy of thePMMA and PEMA materials rendered them effective adhesion promoters forthe liquid repellent coatings that contain surface-segregatedfluorodecyl POSS and enhanced the durability of the liquid repellentcoatings.

Low surface energy fluorodecyl POSS is a promising material forfabricating liquid repellent coatings, but is characterized by a numberof drawbacks in its pure form, including high cost, a tendency todeposit from solution as a rough film, a lack of optical transparency,and poor adhesion to underlying substrates. Blends comprising 0-50 wt %fluorodecyl POSS dispersed in a TECNOFLON, PMMA, PEMA, or PBMA binderhave been made. Each of the shortcomings of pure fluorodecyl POSS filmscan be addressed through dispersion into an appropriately selectedpolymeric matrix.

The liquid wettability of each blend was probed by measuring advancingand receding contact angles of three polar liquids (water, ethyleneglycol, and dimethyl sulfoxide) and three nonpolar fluids(diiodomethane, rapeseed oil, and hexadecane). The resulting contactangle data were concisely represented in the form of wettabilitydiagrams (FIGS. 5D and 6D) in which a geometrically-determined dropsliding parameter (Equation 3) was plotted against a drop pull-offfactor (Equation 5) to intuitively illustrate the relative liquidwettability (or repellency) of each test substrate. Additionalquantitative characterization of the test coatings was completed byusing the Girifalco-Good framework to calculate the individual polar,dispersive, and acidic/basic components of advancing and recedingsurface energy values. While a number of the studied polymer/fluorodecylPOSS coatings were characterized by an advancing surface energy as lowas 9±1 mN/m, the receding solid surface energy values and theirindividual contributions are sensitive to the specific composition ofthe polymeric binder. These variations in the energy contributionsassociated with a receding drop are important because it is low recedinginteractions that minimize pinning of a receding contact line andresistance to both drop sliding (Equation 3) and drop pull-off (Equation5). It was important to consider the individual acidic and basiccontributions, γ_(sv,r) ⁺ and γ_(sv,r) ⁻, because it is the binarysolid-liquid interactions √{square root over (γ_(sv,r) ⁺γ_(lv) ⁻)} and√{square root over (γ_(sv,r) ⁻γ_(lv) ⁺)}, not the solid polarcontribution, γ_(sv,r) ^(p), that influence liquid wettability. Specificacid-base interactions may take place even on surfaces characterized byvery low values of the polar contribution γ_(sv,r) ^(p), because either:(i) γ_(lv) ⁺ or γ_(lv) ⁻ is very large; (ii) a near-zero value ofγ_(sv,r) ⁺ (or γ_(svr) ⁻) makes γ_(sv,r) ^(p) appear negligible eventhough γ_(sv,r) ⁻ (or, γ_(sv,r) ⁺) is significant. It was the low valuesof γ_(sv,r) ^(p), γ_(sv,r) ⁺, and γ_(sv,r) ⁺ that truly distinguishedfluorodecyl POSS as a strongly liquid-repellent material.

The weakest solid-liquid interactions were obtained on PMMA/fluorodecylPOSS and PEMA/fluorodecyl POSS blends with fluorodecyl POSS loadings of20 wt % and above. These PMMA/ and PEMA/fluorodecyl POSS materials werecharacterized by even lower apparent receding surface energy values thanpure fluorodecyl POSS coatings, most likely due to the surface roughnessof the pure fluorodecyl POSS films. The addition of the PMMA or PEMAmatrix phase had a number of other performance benefits besidesfacilitating the deposition of smooth films. These desirable attributesincluded reducing the amount of |expensive fluorodecyl POSS required toprovide maximum liquid repellency, imparting optical transparency tofluorodecyl POSS-based films, and enhancing the adhesion of the liquidrepellent coating to underlying substrates. These improvements inperformance may facilitate the adoption of fluorodecyl POSS-basedmaterials as coatings in liquid repellency applications.

The above-mentioned nanocomposites which are optically transparent mayalso adhere strongly to substrates and resist smudging by fingerprints.Blends containing a relatively high surface energy polymer (e.g.,poly(methyl methacrylate), poly(ethyl methacrylate) (PEMA), poly(butylmethacrylate)) adhere more strongly to surface than those containing thefluoropolymer TECNOFLON, as illustrated in FIG. 11. The 80/20PEMA/fluorodecyl POSS blend was characterized by a low surface energy(about 14 mN/m) calculated from receding liquid contact angles of water,dimethyl sulfoxide, and diiodomethane. This low “receding surfaceenergy” (i.e., high receding liquid contact angles) correlates stronglywith the fingerprint resistance of these coatings, a characteristic thathas not been identified previously as critical to the development ofsmudge-resistant surfaces.

Plots of the advancing and receding liquid contact angles of water,dimethyl sulfoxide, and diiodomethane are provided in FIGS. 5 and 6 forPEMA/fluorodecyl POSS blends as a function of the fluorodecyl POSSloading. The maximum liquid repellency was obtained with a fluorodecylPOSS loading of only 10-20 wt %, a clear benefit from a costminimization standpoint. The fingerprint resistances of a series ofPEMA/fluorodecyl POSS blends were probed using the following test: (1)stearic acid powder was smashed between a tester's thumb and forefinger;(2) the forefinger was then dragged across glass slides coated with testblends, leaving behind a trail of stearic acid powder; (3) this powderwas then blown off using a house air gun operating for 5 seconds from aheight of 3.5 cm; and (4) the substrates were visually examined.Photographs of 4 test surfaces subjected to this stearic acidfingerprinting test are shown in FIG. 12. These images clearly revealthat the 80/20 PEMA/fluorodecyl POSS substrates resisted smudging byfingerprints substantially more than bare glass. This resistance may bederived from the low receding surface energy of the coating.

Other methods and materials for quantifying fingerprint resistance ofcoatings can also be used.

Other embodiments are within the scope of the following claims.

1. A method of making a liquid repellent coating on a non-porous surface, the method comprising: combining a fluoropolymer with a polymer, the polymer being poly(ethyl methacrylate), poly(butyl methacrylate), or both, to form a mixture; and applying the mixture to the non-porous surface to form a coating thereon, the coating being hydrophobic and oleophobic. 2-15. (canceled)
 16. The method of claim 1, wherein the fluoropolymer is fluorodecyl polyhedral oligomeric silsesquioxane.
 17. The method of claim 1, wherein applying the mixture includes spin coating.
 18. The method of claim 1, wherein the polymer further comprises poly(methyl methacrylate).
 19. The method of claim 1, wherein the coating has a receding surface energy that is no greater than 50 mN/m.
 20. The method of claim 19, wherein the coating has a receding surface energy that is no greater than 20 mN/m.
 21. The method of claim 20, wherein the coating has a receding surface energy that is no greater than 15 mN/m.
 22. The method of claim 1, further comprising: introducing nanoparticles to the mixture before applying the mixture.
 23. The method of claim 1, wherein the fluoropolymer is a fluorinated nanoparticle.
 24. A hydrophobic and oleophobic coating prepared in accordance with the method of claim
 1. 